To evaluate in subjects neural adaptation to optically induced simultaneous vision corrections in presence of their natural aberrations.

Methods

A modified Simultaneous Vision simulator was used to produce pure bifocal images. The shift in Perceived Best Focus (PBF, i.e. amount of blur that is perceived as neutral) following adaptation to bifocal images was measured in four normal subjects. Adapting images were real bifocal images of different additions (achieved by combining two Badal channels focused for distance and near: 0.5D, 1.5D, and 3D) and proportions of near/far energy (produced by a spatial light modulator: 100%Blur (B)/0%Sharp (S), 75B/25S, 50B/50S, 25B/75S, 0B/100S). A total of 9 bifocal blur patterns, 3 pure defocus, 1 sharp, and 1 gray adaptation conditions were tested. Test images were 301 pure defocus images, simulated by convolution with 0 to 3D spherical blur of a face (subtending 2 deg at retina). The PBF was obtained with a blur detection task in a QUEST paradigm (subject responded for each test image whether it was sharp or blurred). The PBF shift was calculated as the difference between the PBF following every adapting image and the PBF following gray adaptation. All measurements were performed under paralyzed accommodation and a 5-mm pupil diameter artificial pupil.

Results

The average PBF across subjects was 0.63±0.17D following gray adaptation and 0.51±0.1D following sharp adaptation (natural viewing), with no statistically significant differences (p=0.08) between these conditions. A high statistical significant correlation between the blur level of the adapting images and the shift in PBF (r=0.77, p=0.003). The largest shift in PBF occurred following adaptation to pure defocus (100B/0S: 0.32D±0.02D) and to the bifocal pattern with the largest blur component (75B/25S: 0.19D± 0.05D) for 3 D addition. Adaptation to a 50B/50S bifocal pattern produced the largest PBF shift (0.13D± 0.05D) for a 1.5 D addition. None except one subject experienced significant after-effects following adaptation to25B/75S bifocal pattern.

Conclusions

Our results suggest that subjects can adapt, to a certain extent, to the image degradation produced by simultaneous vision pattern, particularly to patterns with 50%Near/50%Far or 75%/25%-Near or Far. A simultaneous vision simulator is a useful tool to assess potential adaptation effects to bifocal corrections.